This application claims the benefits of Japanese Application No. 11-323135 which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a double-wound band braking device which is used in an automatic transmission, or the like, of a car.
2. Related Background Art
In an automatic transmission of a car or in an ordinary industrial machine, a band braking device is widely used to brake a gear element or a rotating element thereof. Generally, the band braking device applies the brake in such a manner that a friction member is attached to the inner peripheral surface of one steel plate formed in an annular shape to serve as a brake band, and this brake band is contracted by an actuator to thereby tighten up a gear element or a rotary element disposed on the inner side thereof. Recently, there is proposed a double-wound band braking device which uses a double-wound brake band in order to reduce an operational force of the actuator or to improve the braking controllability.
A double-wound brake band 3 is mainly composed of an annular intermediate band 11 and a pair of annular outer bands 15 which are welded and jointed to the free end of the intermediate band 11 through a coupling plate 13 in such a state that the free ends of the outer bands 15 respectively face the free ends of the intermediate band 11, as shown in an example of an automatic transmission of a car in FIG. 13 and FIG. 14 (a view seen from the arrow F in FIG. 13). Friction members 17 and 19 are respectively attached to the inner peripheral surfaces of the intermediate band 11 and the outer bands 15. An anchor bracket 21 which is latched by an anchor pin 5 on the side of the main body casing 1 is welded to the operational end side of the outer bands 15, while an applied bracket 25 for receiving the force in a direction in which the intermediate band 11 and the outer bands 15 are contracted from a push rod 23 of an actuator 7 is welded to the operational end side of the intermediate band 11. In this double-wound brake band 3, when the push rod 23 of the actuator 7 is operated in the direction indicated by the arrow in FIG. 13, the intermediate band 11 and the outer bands 15 are contracted, and the brake is applied on a gear element (hereinafter called xe2x80x9cthe drumxe2x80x9d) 27 which is fitted in the double-wound brake band 3.
Incidentally, in the conventional double-wound brake band 3 described above, the coefficient of elasticity of the single intermediate band 11 is naturally different from that of the paired outer bands 15. For this reason, when receiving a load from the actuator 7, the intermediate band 11 relatively moves (rotates) around a joint portion with respect to the outer bands 15 since an amount of deformation of the intermediate band 11 becomes larger than that of the outer bands 15. This relative movement is not only caused upon reception of the load at the time of braking, but caused due to an initial load at the time of setting. FIGS. 15 and 16 show a state of the double-wound brake band 3 at the time of setting in an exaggerated manner. As seen from these drawings, the operational end side portion of the intermediate band 11 is protruded inward with respect to the outer bands 15 only by the dimensions m. On the other hand, the free end side portion thereof is protruded outward with respect to the outer bands 15 only by the dimensions n. Also, since the intermediate band 11 has the high rigidity at the joint portions thereof with the outer bands 15, an amount of deformation of the operational end side portion is larger than that of the free end side portion. Thus, the dimensions m is larger than the dimensions n.
The double-wound brake band 3 has been manufactured in various dimensions depending on the use or specifications thereof. Thus, the double-wound brake band 3 of large dimensions naturally has a heavy weight. However, in order to reduce the size and the weight of the whole brake band, the plate thickness of the anchor bracket 21 or the size of the anchor pin 5 can not be made large in proportion to the weight of the double-wound brake band 3. For this reason, in the double-wound brake band 3 having large dimensions and heavy weight, the plate thickness of the anchor bracket 21 and the size of the anchor pin 5 are relatively small, so that the brake band 3 becomes unstable due to insufficient fixation when it is set in the main body casing 1. Thus, these members may be inclined with respect to the drum 27.
When the relative movement between the intermediate band 11 and the outer bands 15 or the inclination of the double-wound brake band 3 as described above is generated, there arises a possibility that friction members 17 and 19 which are attached to the inner peripheral surface of the intermediate band 11 or those of the outer bands 15 may be brought into contact with the outer peripheral surface of the drum 27. In this case, when the braking device is incorporated in an automatic transmission of a car, the friction members 17 and 19 are brought into sliding contact with the outer peripheral surface of the drum 27 all the time while the car is running except the time of braking by the double-wound band braking device, which results in various inconveniences including an increase of the cost of fuel for running and deterioration of the surfaces of the friction members 17 and 19 due to frictional heat.
Taking the above circumstances into consideration, an object of the present invention is to provide a double-wound band braking device for preventing unnecessary contact between the double-wound brake band and a rotary member simply and effectively.
In order to solve the above problems, according to a main aspect of the present invention, there is proposed a double-wound band braking device having a double-wound brake band which comprises: an annular intermediate band with a friction surface formed on the inner peripheral side thereof;
a pair of annular outer bands each with a free end secured to face the free end of the intermediate band and each with a friction surface formed on the inner peripheral side thereof;
an anchor portion formed on the operational end side of either one of the intermediate band and the outer bands and is latched on the casing side of the main body; and
an applied portion formed on the operational end side of the other of the intermediate band and the outer bands, for receiving the force in a direction in which the intermediate band and the outer bands are contracted, from an actuator,
and the double-wound band braking device to be used in braking a rotary member fitted in the double-wound brake band, comprising either one of:
deformation amount balancing means for balancing an amount of elastic deformation of the intermediate band and an amount of elastic deformation of the outer bands at a predetermined position; and
center-misalignment correction means for correcting the center-misalignment between the intermediate band and the outer bands.
According to a second aspect of the present invention, in the double-wound band braking device of the main aspect of the invention, at least one of the displacement amount balancing means and the center-misalignment correction means may be a guide which is secured between the central portion in the circumferential direction of the intermediate band and the applied portion, for coming into contact with the outer peripheral surfaces of the outer bands in a sliding manner or a rolling manner.
According to a third aspect of the present invention, in the double-wound band braking device of the main aspect, the anchor portion may be formed on the operational end side of the intermediate band and the deformation amount balancing means may be a hook secured to the anchor portion for latching the outer bands being contracted by a predetermined amount.
According to a fourth aspect of the present invention, in the double-wound band braking device of the main aspect, the deformation amount balancing means may be an elastic member which is interposed between the operational end of the intermediate band and the free end of the intermediate band.
According to a fifth aspect of the present invention, in the double-wound band braking device of the third or fourth aspect, the center misalignment correction means may be a positioning piece which is secured to the outer peripheral surfaces of the paired outer bands in such a manner that it is approximated to or brought into sliding contact with the outer peripheral surface of the intermediate band so as to prevent a relative protrusion of the intermediate band.
According to a sixth aspect of the present invention, in the double-wound band braking device of the main aspect of the present invention, at least either one of the deformation amount balancing means and the center misalignment correction means may be a positioning piece which is secured to the outer peripheral surface of the intermediate band in such a manner that it is approximated to or brought into sliding contact with the outer peripheral surfaces of the outer bands so as to prevent a relative protrusion of the outer bands.
According to a seventh aspect of the present invention, in the double-wound band braking device of the main aspect of the present invention, at least one of the deformation amount balancing means and the center misalignment correction means may be a plurality of positioning pieces interposed between the main body casing and the double-wound brake band.